1. Field of the Invention
The present invention relates to a thin film transistor (TFT) and a method of manufacturing the same, and more particularly, to a thin film transistor (TFT).
2. Description of the Related Technology
In general, flat panel displays (FPD) such as organic light emitting displays (OLED) and thin film transistor liquid crystal displays (TFT-LCD) can be made flexible. In order to make a display flexible, a flexible substrate is used. The flexible substrate may be a plastic substrate or a metal foil substrate.
The plastic substrate is typically made of a synthetic resin. However, when a TFT is formed on the plastic substrate, the substrate may be deformed. Thin films formed on the substrate may also be deformed due to, for example, infliction of moisture and oxygen.
On the other hand, the metal foil substrate, such as stainless steel (SUS) or Ti, has less flexibility than the plastic substrate. However, in a TFT formed on the metal foil substrate, the organic light emitting layer does not deteriorate due to the transmission of moisture and oxygen. In addition, the metal foil substrate can undergo a high temperature process. Therefore, the metal foil substrate can be used for a TFT having a polysilicon semiconductor layer made by a high temperature process.
In general, in order to form TFTs on a conductive substrate, in particular, a conductive thin film formed of SUS or Ti, an insulating buffer layer may be used between the conductive thin film and the TFTs. The TFTs formed over the buffer layer on the conductive thin film has similar electrical and structural properties as silicon on insulator (SOI). At this time, the LTPS obtained by low temperature heating an amorphous silicon layer to crystallize the amorphous silicon layer or by excimer laser annealing the amorphous silicon layer is used as a semiconductor layer that forms the TFTs.
In manufacturing the conventional TFT, impurities such as Cr, Fe, Ni, and C of the substrate are diffused into the semiconductor layer through the buffer layer during a predetermined thermal annealing process performed on the LTPS.